Calcium (Ca) ions play a central role in determining the waveshape of the action potential and the strength of contraction in cardiac muscle. The long term objectives of this research are 1) to define the cellular and molecular basis for the control of cytosolic Ca in normal and diseased cardiac muscle and 2) to characterize specific membrane proteins involved in Ca homeostasis and determine how they are regulated during normal growth and during the response to hemodynamic overload states which cause dysfunctional hypertrophy and lead to congestive heart failure (CHF). These issues are of particular importance in CHF because in this condition the electromechanical properties of the heart are abnormal. This study will define the cellular defects in Ca homeostasis which contribute to these abnormalities. The specific aims of this research are: 1) To move fully characterize a recently developed animal model of pressure overload- induced LV hypertrophy and failure. 2. To define the changes in electromechanical properties and Ca homeostasis of myocytes isolated from failing feline LV. 3) To determine if changes in excitation-contraction coupling play a role in the weakened contractile state of failing myocytes. These studies will determine if changes in "L type" Ca current and/or Ca- induced Ca release can explain the dysfunctional contractile of the sarcoplasmic reticulum produces the alterations in diastolic Ca and systolic Ca transients that are observed in failing myocytes. 5. To determine if the diminished beta-adrenergic responsiveness of the failing heart results from alterations in either B1- and/or B2-receptor density or effector coupling. Myocytes isolated from normal and failing (progressive LV pressure overload) feline ventricular muscle will be used. Ca currents will be measured using Indo-1. Pharmacological and molecular approaches will be used to study beta-adrenergic receptors. These experiments should provide new insight into the role of abnormal Ca homeostasis in CHF.